The present invention relates to a voice packet assembling/disassembling apparatus which assembles and disassembles voice packets in a voice packet communications system.
A voice packet communications system and apparatus are disclosed in "Voice packet system", K. Saito et al, Electrical Communication Laboratories Technical Journal of NTT, Vol. 38, No. 3, pp. 231-237, 1989.
FIG. 3 illustrates a schematic view of a voice packet communications system. In FIG. 3, voice terminal 1, such as a telephone set, is connected to a Private Branch Exchange (PBX) 2. The PBX 2 is connected to a voice Packet Assembler/Disassembler (PAD) 4 through an Interface (I/F) 3 which multiplexes 30 PCM channels. Interface 3 conforms to TTC of Japan or JJ-20.10, JJ 20.11 and JJ 20.12.
Voice signals input from the voice terminal 1 reach the voice PAD 4 via PBX 2 and I/F 3. In the voice PAD 4, input voice signals are coded to embedded ADPCM. The voice PAD 4 is connected to a packet multiplexer 6 via I/F 5 conforming to CCITT Recommendation X.21. The packet multiplexer 6 is connected to another packet multiplexer via high speed digital switch 7.
FIG. 4 illustrates a prior interleave process for assembling/disassembling packets containing upper bits and lower bits, respectively. In FIG. 4, the coded embedded ADPCM voice data are divided into upper bits and lower bits for each sample. Voice data for more than one sample are collected and assembled into respective packets for upper bits and for lower bits by the interleave process. Then the packets are multiplexed in the voice PAD 4.
Although the above explanation is concerned with transmission, the process of reception is generally the same, as explained below. The voice PAD 4 disassembles the received packets to coded embedded ADPCM voice data for each sample, decodes these data to voice signals, and sends them to the PBX 2.
FIG. 5 illustrates a prior voice packet assembling/disassembling apparatus which assembles and disassembles a voice packet. In FIG. 5, I/F 3 is connected to a PBX interface 8, and the PBX interface 8 is connected to each CODEC 9-1 to 9-30, and each CODEC 9-1 to 9 30 is connected to corresponding PAD 10-1 to 10-0. And all PADs 10-1 to 10-30 are connected to the packet multiplexing part 15 which contains a multiplexer 11 for multiplexing the voice signals, a CPU 13 for controlling all the blocks in the PAD 4, a data memory 12 and a line control circuit 14 which sends or receives packets.
At the transmitting side, voice signals from I/F 3 input to the CODECs 9 are provided for each channel via PBX interface 8. Each CODEC 9-1 to 9-30 codes the voice signals and sends them to PAD 10-1 to 10-30 provided for each channel. Each PAD 10 samples the coded signals and discriminates the upper bits from the lower bits. All upper bits are collected to upper blocks and lower bits are collected to lower blocks. Voice packets are assembled from these blocks by adding a header and are sent to the multiplexer 11. The multiplexer 11 multiplexes the voice packets received from each PAD 10 and stores them into the data memory 12. CPU 13 reads the voice packets stored in the data memory 12 and provides them to the line control circuit 14. The line control circuit 14 sends the voice packets to I/F 5 in accordance with the layer 2 protocol.
On the other hand, at the receiving side, voice packets received from I/F 5 are input to the PAD 10 provided for each channel via multiplexing part 15. Each PAD 10 disassembles the voice packets into packets containing upper blocks and other packets containing lower blocks. Each PAD 10 rearranges these packets to the coded voice data for each sample and then transmits them to its corresponding CODEC 9. Each CODEC 9 decodes the coded voice data into voice signals and sends them to I/F 3 via the PBX interface 3.
But, in the prior voice packet assembling/disassembling apparatus, it was necessary to provide PAD parts for each channel. In the result, the configuration of the PAD parts becomes very large and expensive.